In an electrographic recorder of the type described in the Kotz U.S. Pat. No. 3,816,840 issued June 11, 1974 and the Lunde U.S. Pat. No. 3,879,737 issued Apr. 22, 1975, a rotating magnet operates in conjunction with magnetic toner particles and a moving recording medium such as paper to leave marks or dots of toner on the paper which, desirably, appear as a continuous trace or line thereon. More specifically, the rotating magnet is placed within a shell and magnetic toner particles are placed around the shell. The paper travels near the shell over a conductive nonmagnetic surface. A stylus is placed adjacent the paper on the shell and each time a "north" or "south" pole of the rotating magnet is in the vicinity of a stylus, the magnetic toner particles form a "tree" which bridges the gap between the shell and the paper so that the toner particles touch the paper. When a source of voltage of sufficient magnitude is connected between the stylus and the conductive surface, the magnetic force holding the toner particles to the shell is overcome and a few of the particles attach to the paper as a "dot" which is later permanently "fixed" thereto.
Unfortunately, the toner particles only form a "tree" that bridges the gap to the paper when the "north" or "south" poles of the rotating magnet are in the vicinity. Between the poles, the toner particles "lie down" and it is not possible to leave a mark or "dot" on the paper.
It has been found that the tree is formed about fifty percent of the time in the prior art devices while the toner lies down about fifty percent of the time. Since it is desirable to leave a series of dots on the paper which are touching one another to produce a continuous line, the speed at which the paper moves is somewhat restricted. More particularly, Vmax=df where Vmax is the maximum velocity of the paper to allow the edges of the dots to touch, d is the linear distance across the dots (they may not be circular) and f is the frequency of pole passages of the rotating magnet. Because of mechanical limitations, f is a very real and limiting value so that the paper velocity may have a practical limit of less than ten inches per second for low resolution to less than three inches per second for high resolution. With lower paper speeds, the dots will more and more overlap which is desirable but with higher paper speeds, significant gaps appear between dots which is undesirable.